In many of vehicle seats, there has been widely used a fold-down type of rear seat wherein the seat back thereof can be folded forwardly and downwardly in order to widen a load or luggage space (luggage room) behind the rear seat. (For example, reference is made to the Japanese Laid-Open Patent Publication No. 2008-296686)
In general, according to such fold-down rear seat, a lock mechanism is provided to an upper end region of a lateral wall of the seat back thereof, and a latch rotatably provided in that lock mechanism may be engaged with a striker fixed on a side wall of a vehicle, in an embracing manner, to thereby lock the seat back at an upright position where the seat back is set in a vertically extending state (i.e. a position where a seat occupant can sit on the rear seat). With this locking operation, the seat back is prevented from being folded forwardly and downwardly from the upright position.
Basic construction of the above-stated lock mechanism is known well. Briefly stated, the lock mechanism is provided as one pre-assembled unit which comprises a base plate, a cover plate and a latch, such that the latch is rotatably interposed between the base plate and the cover plate and that a guide surface defined in the outer edge of the latch is exposed from a cut-away portion formed in those base and cover plates. Further, the latch is formed with a lock groove which assumes a shape of an elongated hole, and such lock groove is defined in the latch at a point behind or at the rear of the guide surface. A biasing force is applied to the latch, so that the lock groove of the latch is kept in engagement with and over the striker in an embracing manner, thereby locking (or retaining) the seat back of the rear seat at the upright position.
A direction of the afore-said biasing force, therefore, corresponds to a direction in which the lock groove embracingly engages the striker. Hence, for example, upon pressing an unlocking button for lock-off operation to unlock the latch temporarily, the latch may be rotated in a direction to overcome such biasing force to disengage the lock groove of the latch from the striker (which means that the seat back can be unlocked), thereby permitting the seat back to be folded downwardly from the upright position.